MoreHappens every year: You're all gung ho in the beginning of the summer, hitting the gym like it's your job and dutifully counting calories. After all, you have the big bikini body reveal to prepare for! But once the season hits its stride, it's easy to fall off the wagon and onto a lawn chair—and before you know it, the heaviest thing you're hoisting is an icy cocktail.

Fortunately, tearing off that cover-up with confidence doesn't mean choosing between having fun and staying fit. The key to scoring a hot body? Committing to a plan that's easy to fit into your busy summer schedule (we're talking 30-minute workouts here) and lasts exactly 21 days. Why? Experts say you can start to form a habit in as little as three weeks, and as anyone who's ever been hooked on something knows, habits are hard to break. In other words, once you complete this program (which has built-in days for rest and recovery—yay!), you'll be motivated to keep going.

How the Plan Works
Each week, you'll do six workouts: two total-body toning routines, two fat-blasting interval workouts, and two easy, results-enhancing recovery sessions. It doesn't matter what order you do them in, as long as you do them. (The goal is to get used to penciling in a little exercise each day, which helps you form a workout habit.) The remaining day is your no-excuse-needed day off—enjoy it!

Total-Body Toning Workouts (two per week)
Exercises 1-6

These fast-paced strength circuits are designed to target multiple muscle groups at once so you can build lean muscle, rev your heart rate, and torch a ton of calories in a short amount of time. Best of all, you'll fire up your metabolism and continue to burn calories 24 to 48 hours after your workout is done.

Do the first pair of exercises as instructed, resting for 30 seconds between each move. Continue until you've finished all three pairs. During week one, complete one set of each pair. During weeks two and three, complete two sets.

Fat-Blasting Interval Workouts (two per week)
Exercises 7-9

This is your cardio fix. These interval-training workouts utilize high-intensity body-weight exercises to get your heart rate up, burn calories, and supercharge your metabolism. Do these three moves back-to-back, completing as many reps as you can in the prescribed amount of time. Rest for one to two minutes, then repeat. During week one, do each move for 20 seconds and complete five intervals. In week two, do six intervals of 30 seconds each, and in week three, do seven intervals of 40 seconds each.

The key to seeing results: Push yourself as hard as you can while keeping good form. Each time you do the routine, try to increase the number of reps you complete in the amount of time given.

Results-Enhancing Recovery Workouts (two per week)
Exercises 10-13

This quick, stretch-focused routine is designed to balance your high-intensity strength and cardio days and help create that enviable long and lean look. These four moves will stretch your chest and strengthen your upper back (to improve your posture), as well as activate your glutes, engage your core, and stretch your hip flexors (all of which help to correct postural imbalances and flatten your belly). Do these moves two or three times in order.

Exercise 1Plank with Alternating Leg Lift

Get into a plank position, with your forearms on the ground, elbows directly under your shoulders, and legs extended straight behind you, feet hip-width apart. Your body should form a straight line from your shoulders to your ankles, and your core should be braced. Keeping your hips parallel to the floor, squeeze your glutes to raise your right foot a few inches into the air. Hold for two seconds, then lower your foot. That's one rep. Repeat with your left foot. Continue alternating for 12 total reps.

Exercise 2Wood Chop with Resistance Band

Stand to the right of a resistance band (secured a few feet above your head). With your feet hip-width apart, rotate your torso slightly to the left and grab the handles with both hands so that your arms are straight and above your left shoulder. Keeping your arms straight and back flat, pull the handles across your body to the outside of your right knee. Pause, then slowly return to start. That's one rep. Do 12 to 15 total, then switch sides and repeat.

Exercise 3Dumbbell Squat and Overhead Press

Hold a pair of dumbbells at your shoulders, standing with your feet hip-width apart. Push your hips back and lower into a squat, keeping your chest upright and your knees over your toes. As you push through your heels to return to standing, press the dumbbells overhead. Lower the weights to return to the starting position. That's one rep. Do 12 to 15.

Exercise 4Romanian Deadlift

Hold a pair of dumbbells in front of your thighs, feet hip-width apart, knees slightly bent. Bend at your hips to lower your torso until it's almost parallel to the floor, keeping your back flat and the weights close to your legs. Squeeze your glutes as you slowly return to standing. That's one rep. Do 12 to 15.

Exercise 5Bent-Over Row

Standing with your feet hip-width apart and knees bent, hold a pair of dumbbells so your palms are facing each other and bend forward from the hips, as shown. Pull your shoulder blades together and row the weights toward your chest. Return to start. That's one rep. Do 12 to 15.

Exercise 6Dynamic Lunge

Stand with your arms at your sides, feet hip-width apart, chest lifted. Step forward with your right leg and bend both knees to lower yourself as far as you can. Push off your right foot and return to start. Repeat, stepping forward with your left leg. That's one rep. Do 12 to 15.

Exercise 7Mountain Climber

Assume a pushup position with your hands directly under your shoulders and your body forming a straight line from your head to your ankles. Keeping your core tight and back flat, bend your right knee and raise it toward your chest. Reverse the movement to return to start, then repeat with your left leg. Continue alternating.

Exercise 8Lateral Shuffle

Stand with your feet hip-width apart, knees bent, chest upright, and elbows bent at a 90-degree angle. Take a wide step to the left, then quickly bring your right foot to meet your left. Then switch directions, stepping your right foot out to the side. Continue going back and forth.

Exercise 9Jump Squat

Place your hands behind your head, elbows out, and stand with your feet hip-width apart. Push your hips back and bend your knees until your thighs are nearly parallel to the floor, keeping your chest up. Jump as high as you can, then immediately lower into the next rep.

Exercise 10Hip Flexor Stretch

Kneel on your right knee, and place your left foot flat on the floor in front of you. Keep your torso upright and rest your hands on your hips. Gently push your hips forward as far as you comfortably can, while keeping your torso upright. You should feel a stretch in the front of your right hip. Hold for 30 seconds, then switch leg positions and repeat.

Exercise 11Double Hip Extension

Lie on your back and bend your knees so that your feet are flat on the floor. Slide your arms out to your sides at 45-degree angles, palms facing up. Tighten your core, then squeeze your glutes to lift your hips an inch off the floor. This is the starting position. Raise your hips toward the ceiling until your body forms a straight line from shoulders to knees. Pause, then lower to the starting position. That's one rep. Do 10.

Exercise 12Standing Chest Stretch

Stand with your left side facing a wall. Bend your left elbow 90 degrees, and place your palm and forearm on the wall. Lean your torso forward to stretch your chest. Hold for 30 seconds, then turn around and repeat with your right arm.

Exercise 13Floor I-Position Raise

Lie facedown on the floor. Extend your arms above your head and rest them on the floor, keeping them straight and in line with your shoulders, palms facing each other and thumbs pointing toward the ceiling. Your body should form a straight line from your feet to your hands. Squeeze your shoulder blades together and down to raise your arms a few inches off the floor, keeping them straight. Pause, then slowly lower back to the starting position. That's one rep. Do 10.